Doors for homes and offices are often metal. Metal doors are fire resistant. Due to their fire resistance, insurance companies encourage their use. Manufacturers of metal doors are now able to provide insulation that reduces moisture condensation problems encountered in the past. Manufacturers have also learned how to form outer surfaces that are attractive and durable.
Wood inserts are placed inside the doors for mounting latches and locksets and also for mounting dead bolts. The wood blocks must be free of knots and blemishes. In addition, the wood must hold screws that secure face plates for latches and dead bolts. If a wood block splits when a screw is screwed into it, the doors is essentially destroyed. Once insulation is injected into the hollow interior of the door, the wood blocks cannot be replaced.
Wood suitable for making metal door insert blocks is scarce. Much of the available wood has knots that preclude its use for making door inserts. Some wood is too soft to hold the required screws for attaching face plates. Other available woods are brittle and tend to split when screws are inserted into them. As a result of the scarcity of suitable wood for door inserts and increased demand for metal doors, the wood that is available has become expensive.
Manufacturers of metal doors have taken steps to conserve wood. Wood can be conserved by reducing the size of the blocks that are inserted. When the size of the wood block inserts is reduced, an individual block can only accommodate a latch and lockset with one predetermined set back distance. The set back distance is the distance from the edge of the door to the center of the latch or dead bolt control members. The wood block insert for the dead bolt also accommodates dead bolts with one specific size. As a result, metal door manufacturers have to maintain a supply of several wood block inserts and metal door retailers must maintain an inventory of doors that will accommodate various latch and lock assemblies as well as a variety of dead bolts.